How to get error message of validator from TextFormField

Question

I want to get error message programmatically to display somewhere else. Example error show Text is too short, I can get it by using _formKey.currentState... . How to get there?

Form(
  key: _formKey,
  child: TextFormField(
    validator: (value) {
      if (value == null || value.isEmpty) {
        return 'Please enter some text';
      }
      if (value.length < 5 ) {
        return 'Text is too short';
      }
      return null;
    },
  ),
)